A product that is obtained by carrying out a predetermined treatment to a molded powder compact manufactured by compressing magnetic powder is commonly known. Examples of such a product include magnetic cores (metal powder cores and ferrite cores) included in coiled components such as inductors, transformers, and chokes. Such magnetic cores are produced in such a manner that a molded powder compact is manufactured by compressing ferrite or metal magnetic powder, and then the molded powder compact is annealed and sintered by carrying out a heat treatment.
Further, a drum-shaped molded powder compact in which a shaft is provided between a pair of flanges is known as molded powder compact. A drum-type magnetic core (drum core) obtained by heat treating the drum-shaped molded powder compact, along with a coil wound around the shaft, constitutes a coiled component described above. Such a molded powder compact is manufactured by carrying out machine processing to cut a molded powder compact having a simple shape such as a circular cylinder or a rectangular solid (cf. Patent Document 1). In recent years, however, various attempts have been made in order to reduce processing by near-net-shape forming.
FIG. 9 shows a cross-section of a mold that is used for near-net-shape forming of a molded powder compact. With this, a molded powder compact 1 having a shaft 13 between a pair of flanges 11, 12 as shown in FIG. 1 is provided. The mold includes a pair of punches 91 that face each other in a pressure direction (an up-down direction in FIG. 9), and tubular dies 92 that are disposed on both side of the punches. Each of the punches 91 is provided with a flange forming portion 93 and a shaft forming portion 94. Tip end portions 94a of the shaft forming portion 94 are formed flat so as to ensure their thickness. This also applies to tip end portions of the flange forming portion 93. This is because there is a concern, for example, for damages due to poor strength when the tip end portions are pointed.
However, when the molded powder compact 1 is manufactured using the mold described above, corner portions 13A-13D of the shaft 13 have an angular shape as shown in FIG. 1, and therefore it is necessary to carry out chamfering in order not to damage a coil when winding. Further, even if chamfering is not necessary, there is a case in which it is necessary to remove burrs occurring at the corner portions 13A-13D. In particular, magnetic powder made from a soft and highly malleable metal such as pure iron and magnetic powder with fine grain diameter easily get into gaps between the punches and the dies to produce burrs. In view of the above circumstances, it is necessary to carry out treatments, such as chamfering and burring (hereinafter referred to as edge processing), to corner portions of a molded powder compact.